JPH04350127A - Production of steel plate and steel sheet excellent in high temperature characteristic - Google Patents

Abstract

PURPOSE:To produce hot rolled steel plate and cold rolled steel sheet excellent in high temp. strength characteristics by subjecting a slab of a steel having a specific composition where respective contents of B, Nb, Ti, and V are controlled to heating up to a specific temp. and to hot rolling or further to cold rolling and also specifying subsequent conditions. CONSTITUTION:A slab of a steel having a composition consisting of, by weight, >0.008-0.15% C, <=1.00% Mn, 0.01-0.10% Al, 0.0002-0.005% B, 0.004-0.12% Nb, 0.01-0.10% Ti and/or 0.02-0.30% V, and the balance iron with inevitable impurities is prepared. This steel slab is heated up to >=1050 deg.C and hot-rolled at a finishing temp., preferably, of >=Ar3, or, cold rolling is done after hot rolling and the resulting steel sheet is heated at a rate of >=1 deg.C/S and annealed at a temp. between the recrystallization temp. and 1000 deg.C. By this method, the hot rolled steel plate and the cold rolled steel sheet remarkably excellent in high temp. strength characteristics and having extremely superior workability and weldability can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing steel sheets with excellent high-temperature strength properties.

0002

2. Description of the Related Art Heat-resistant materials are required to have little strength loss at high temperatures and to have excellent oxidation resistance. The decrease in strength of a steel plate due to an increase in temperature is greater for steel plates with higher strength at room temperature, and studies are being conducted to reduce this decrease, that is, to improve high-temperature strength characteristics. For example, in Japanese Patent Application Laid-open No. 57-35623, Mo, Cr, V or N
It has been proposed to add b to the steel sheet and slowly cool it after hot rolling to change the steel structure to ferrite + pearlite or ferrite + pearlite + bainite, thereby obtaining a steel sheet with excellent high-temperature strength as hot-rolled. According to this method, a heat-resistant material with excellent high-temperature strength can be obtained without performing heat treatment after hot rolling. By the way, due to the revision of the Building Standards Act in 1988, steel materials for construction are required to have higher strength than before at high temperatures, and there is also a strong demand for buildings to be taller, and from the perspective of ensuring safety. It is also necessary to further improve high-temperature strength.

0003

[Problems to be Solved by the Invention] Generally speaking, the strength of heat-resistant steel decreases to less than 2/3 of its strength at room temperature when it reaches high temperatures, for example, 600°C or higher, and as mentioned above, the strength decreases at room temperature. The higher the strength of a steel plate, the greater the decrease in strength at high temperatures. This tendency is common to conventional steel plates,
It is important to develop steel sheets with improved high-temperature strength properties. In order to obtain high temperature strength characteristics, the above-mentioned Mo, Cr, V, N
A possible measure is to increase the amount of b added, but increasing the amount of alloying elements added causes problems such as deterioration of weldability, deterioration of workability, deterioration of toughness, and further increases in cost. The object of the present invention is to stably obtain a steel sheet at a low cost, which has high strength but has little strength loss due to high temperature, and has good workability, weldability, etc.

0004

[Means for Solving the Problems] In order to stably obtain a steel plate with excellent high-temperature strength properties at a low cost, the present inventor conducted experiments and studies, and found that the present inventors combined Nb and B, and further added Ti and V. By containing one or two types and specifying the heating temperature of the steel billet, a synergistic effect occurs, and even though the amount of the added element is small, the high-temperature strength properties are particularly excellent, and the workability and weldability are also good. It was discovered that a steel plate with a high quality can be obtained. The present invention was made based on this knowledge, and the gist thereof is, in weight%, C: more than 0.008 to 0.15%, Mn: 1.00% or less, Al: 0.01 to 0.10. %, B: 0.0002-0
．． 005%, Nb: 0.004-0.12%, and T
i: 0.01-0.10%, V: 0.02-0.30%
A hot-rolled steel sheet with excellent high-temperature strength characteristics, which is produced by heating a steel billet containing one or two of the following, the remainder consisting of iron and unavoidable impurities to a temperature of 1050°C or higher and hot rolling it. Another feature of the production method is that after the hot rolling, the product is cold rolled, heated at 1°C/S or more, and annealed at a temperature above the recrystallization temperature and below 1000°C, which has excellent high-temperature strength properties. The method for manufacturing cold-rolled steel sheets.

Next, the present invention will be explained in detail. First, the reason for limiting the steel components of the present invention will be described. C
is a necessary component for interacting with added alloying elements to form carbides and improve high-temperature strength properties, and is required in an amount of more than 0.008% to exhibit its effects. On the other hand, if the content increases, the strength at room temperature will increase and the workability and weldability will deteriorate, so the content should be 0.15% or less. Mn is contained in order to prevent hot embrittlement due to the unavoidably contained S, but if the amount is too large, the strength at room temperature becomes too high for a construction steel plate and the workability deteriorates, so the content is limited to 1.00% or less. Al is contained in an amount of 0.01% or more in order to deoxidize molten steel and improve the yield of added alloying elements, but on the other hand, when the content increases, it causes an increase in oxide inclusions, and the above-mentioned effect becomes saturated. Therefore, it should be 0.10% or less. In the present invention, B, N
b Furthermore, one or both of Ti and V are contained in combination in order to reduce the decrease in strength at high temperatures and to obtain high temperature strength characteristics. Even if these elements are contained alone, the strength does not increase much, but as mentioned above, the combined addition of B and Nb and the addition of one or two of Ti and V improves high-temperature strength properties, such as at high temperatures of 600°C or higher. Even if the temperature increases, there is little decrease in strength and high strength can be obtained. To obtain this effect, B is 0.000
2% or more, Nb 0.005% or more, Ti 0.05%
The above V needs to be 0.05% or more. On the other hand, if these contents increase, the strength at room temperature will become too high, and the high temperature strength property improvement effect will be saturated, resulting in high costs.
B is 0.005%, Nb is 0.12%, Ti is 0.15%
% and V each have an upper limit of 0.30%. These B,
The effect of the combined inclusion of Nb, Ti, and V is that B, Nb
Both act together as structure-refining elements to refine the structure, and the structure refinement contributes to the fine precipitation of NbC and TiCVC, resulting in large precipitation strengthening.
It is thought that C, TiC, VC, and solid solution B suppress the movement of dislocations and grain boundaries in the steel, thereby preventing softening due to high temperatures.

[0006] In the present invention, a steel piece containing the above components and the remainder consisting of iron and unavoidable impurities is heated prior to hot rolling.
C, VC In order to further refine the structure, the heating temperature of the steel slab is set to 1050° C. or higher. There is no specific need for hot rolling after heating, but to obtain good workability, the finishing temperature should be set to Ar3.
It is preferable to set it as above. The winding temperature in hot rolling is not required to be specific and is arbitrary. When producing cold rolled steel sheets, hot rolled coils are descaled, then cold rolled and annealed. There is no need to limit the rolling reduction rate of cold rolling. For annealing, the heating rate was set at 1°C/1°C to ensure high-temperature strength.
Must be S or higher. Further, the upper limit of the annealing temperature is set to 1000° C. from the viewpoint of ensuring high-temperature strength characteristics. Further, after hot rolling or cold rolling, oxidized scale on the surface of the steel sheet can be removed and various platings or paints can be applied.

[0007]

[Example] Next, an example will be described. Table 1 shows the steel composition of the test materials, and Table 2 shows the manufacturing conditions. The tensile strength (TS) and yield strength (PS) of the obtained hot-rolled steel sheets and cold-rolled steel sheets at room temperature (30° C.) and 600° C. were measured, and the results are shown in Table 3. As can be seen from this example, it is clear that according to the present invention, the strength at 600° C. is high and the high temperature strength properties are excellent.

[0008]

[Table 1]

[0009]

[Table 2]

0010

[Table 3]

[0011]

[Effect of the invention] As described above, the synergistic effect of the combined addition of Nb and B, the selective addition of Ti and V, and the specific conditions of the heating temperature of the steel billet, as well as the specific conditions after cold rolling, , hot-rolled steel sheets and cold-rolled steel sheets with particularly excellent high-temperature strength properties and extremely good workability and weldability can be obtained.

Claims (2)

[Claims] Claim 1: In weight%, C: more than 0.008% to 0.15% Mn: 1.00% or less Al: 0.01 to 0.10% B: 0.0002 to 0.005% Nb: 0 .004-0.12% and Ti: 0.01-0.10% and V: 0.0
A steel billet containing 2 to 0.30% of one or two kinds, with the remainder consisting of iron and unavoidable impurities, is heated to a temperature of 1050°C or higher and hot rolled. An excellent manufacturing method for hot rolled steel sheets. Claim 2: In weight%, C: more than 0.008% to 0.15% Mn: 1.00% or less Al: 0.01 to 0.10% B: 0.0002 to 0.005% Nb: 0 .004-0.12% and Ti: 0.01-0.10% and V: 0.0
A steel billet containing 2 to 0.30% of one or two kinds, with the balance consisting of iron and unavoidable impurities, is heated to a temperature of 1050°C or higher, cold rolled, and then cold rolled. ℃
A method for producing a cold-rolled steel sheet with excellent high-temperature strength characteristics, characterized by heating at a temperature of /S or more and annealing at a temperature of not less than a recrystallization temperature and not more than 1000°C.